1. Field of the Invention
The present invention relates to an AM receiver and an FM receiver to be mounted on a vehicle. In particular, the present invention relates to a radio receiver which reduces differences in an audio signal output based upon differences in degree of modulation among different broadcasting stations when an FM broadcast is received.
2. Description of the Related Art
Heretofore, FM receivers have been used as radio broadcasting receivers mounted on vehicles. On a transmitting side, a frequency of a carrier wave is modulated by a modulation signal and transmitted. The transmitted signal is received on a receiving side. The frequency modulated signal is converted to an amplitude modulated signal. Furthermore, the amplitude modulated signal is demodulated and outputted as an audio signal. Due to differences in degree of modulation among different broadcasting stations, the output level sometimes changes whenever a station was selected.
In the case where the degree of modulation is significantly different among respective broadcasting stations, the tone level is markedly changed in conventional radio broadcasting receivers whenever a station is selected, as described above. Each time, a sound volume adjustment is needed. In the case of an appliance mounted on a vehicle, however, it is an immense work for a driver to conduct the sound volume adjustment each time. Furthermore, if the gain of the receiver is continuously controlled for the sound volume adjustment, there is sometimes a feeling of fluttering in sound.
An object of the present invention is to provide a radio broadcasting receiver to be mounted on a vehicle, which overcomes the above described drawbacks of the conventional radio broadcasting receiver mounted on a vehicle, which automatically conducts sound volume adjustment when a station is selected, and which can receive nearly the same sound volume irrespective of the station selected.
According to an aspect of the present invention, there is provided a radio broadcasting receiver having an auto tuning means and a digital signal processor, wherein the digital signal processor include a detection means for detecting a maximum value of a received signal output for each of a plurality of broadcasting stations selected during station selection, a storage means for storing a detected maximum value of a received signal output of each of the broadcasting stations, a computation means for calculating a mean value of a plurality of stored maximum values of received signal outputs, and a means for calculating an output gain on the basis of a maximum value of a received signal output of a broadcasting station to be received and the mean value, and wherein there is provided a means for conducting a gain control upon station selection according to an output of the digital signal processor so as to instantaneously bring the received signal output closer to the mean value.
In the above described radio broadcasting receiver, the mean value can be calculated for only a selected broadcasting station among receivable broadcasting stations as the plurality of broadcasting stations. If a selected broadcasting station has newly joined, the mean value can be recalculated.
In the above described radio broadcasting receiver, the storage means can update the storage of the plurality of maximum values of received signal outputs as occasion demands, and the update time can be freely set by a designer on the basis of results of field tests.